Dissertation
Both, A.J. 1995. Dynamic simulation of supplemental lighting for greenhouse hydroponic lettuce production. Ph.D. Dissertation. Cornell University Libraries, Ithaca, NY 14853. 172 pp.
Abstract
During an eight month period, hydroponic lettuce growth experiments, consisting of 35 different supplemental lighting treatments, were conducted in five identical greenhouse sections in order to: (1) determine how supplemental lighting can be used to ensure consistent and timely year-round greenhouse lettuce production in New York State, and (2) provide greenhouse growers and researchers with a computer simulation program to study the effects of different daily integrated light levels, indoor temperature, and plant spacing on the growth and development of lettuce. The daily integrated photosynthetically active radiation (PAR) was kept constant during each of the treatments by supplementing the solar PAR with PAR from 400-Watt high pressure sodium (HPS) lamps. Among treatments, daily PAR varied between 4 and 22 mol-m-2-d-1. The indoor greenhouse environment was computer controlled and carbon dioxide enrichment (up to 1000 ppm) was used during the light period, but only when no ventilation was needed to maintain the temperature set point. The temperature was maintained at 24 and 18.8ºC during the light and dark periods respectively. During the first 11 days, the lettuce seedlings were kept in a growth chamber under fluorescent lamps. After transplant, the plants remained 24 days in the greenhouse. Maintaining a daily PAR of 17 mol-m-2-d-1 in the greenhouse resulted in a marketable lettuce head with a fresh weight of 150 grams (nearly 7 grams of dry weight) at 35 days after seeding. Lettuce tipburn was prevented using an overhead fan, which blew ambient air downward onto the lettuce plants. The computer simulation program predicts dry weight production based on environment conditions in the greenhouse and plant parameters extracted from the literature. The universal crop growth model SUCROS87 was adjusted and incorporated in the simulation program. Using long-term average daily solar radiation data collected for Ithaca, NY, the simulation model successfully predicted dry weight production compared to plant dry weights measured during growth trials, which were performed at Cornell University. The simulation program will be a helpful tool for commercial lettuce growers and future research.
